The present invention involves a computer pointing stick implementing capacitive sensors.
Pointing devices are an essential component of modern computers. The pointing device allows the user to move a cursor on the display of a computer. While the mouse is still the most common type of pointing device, the xe2x80x9cpointing stickxe2x80x9d has become more popular in recent years. These pointing devices consist of a small analog joystick usually between the keys of a keyboard; for example see U.S. Pat. No. 5,521,596 to Selker. One typical implementation of a pointing stick consists of a post placed on top of a number of force sensing resistors (FSR), but there are other possible implementations. While FSR""s are simple and well-known technology, pointing sticks that use FSR""s suffer several drawbacks. First, sticks that use FSR""s require a large number of additional electrical components to amplify their signals to a measurable level. Second, most FSR implementations are quite susceptible to external noise sources. Third, FSR""s may be more expensive and less rugged than other sensing methods. Fourth, FSR""s may be quite susceptible to changes in temperature. Capacitive sensors are well known in the art, and have been disclosed for use in pointing devices. For example, U.S. Pat. No. 5,521,596 discloses a capacitive touch pad for use as a pointing device. Capacitive sensors can also be used to sense force. Force sensing capacitors (FSC) can be used to implement a pointing stick in ways analogous to the use of FSR""s. Capacitive pointing sticks offer several benefits over the use of FSR""s. First, capacitive pointing sticks can be implemented with very few electrical components other than the sensing ASIC, allowing for a smaller and less expensive device. Second, capacitive sensors can also be made less susceptible to external interference. Third, FSC""s can be made to be more rugged than FSR""s and they are much more resistant to changes in temperature than FSR""s.
The purpose of the present invention is to create a device that uses capacitive sensing in a pointing stick and to define some of the details of that implementation.
The present invention is directed to the use of a capacitive sensor to implement a pointing stick. The sensor element can assume a number of different embodiments as discussed below, their common element being the use of a capacitive rather than resistive sensor for implementation.